YSM Issue 96.2

FEATURE
Bioelectronics
CYBORG ZEBR AFISH
BY NATHAN MU
USING THE BODY TO GROW FLEXIBLE ELECTRODES
The human body is a machine. At a
fundamental level, it depends on
electrical currents within cells and
electrical signals between cells to function.
So, in a sense, the body produces its own
electricity. But what happens if this power
gets unplugged? This is the problem that
researchers have faced in trying to cure
diseases such as Parkinson’s, Alzheimer’s,
epilepsy, and depression. In the brain—
where electrical signaling is paramount—
any small "unplugging" can throw off the
system of electrical currents and quickly
lead to improper function. Without a way
to fix an improper pattern of electrical
signaling, that part of the brain will slowly
lose its charge and fizzle out, leading to the
visible symptoms of these diseases.
A team led by organic bioelectronics
researchers Xenofon Strakosas and
Hanne Biesmans of Linköping University
in Sweden may be on track to develop
a viable solution to this problem. They
have targeted this issue of restoring
dysfunctional electrical pathways by
harnessing the body’s chemistry to form
an electrode, or electrical conductor
that helps produce a current, within the
IMAGE COURTESY OF UC SAN DIEGO
Researchers have developed brain sensor implants
that can detect electrical signals.
brain. “The really cool thing about this
electrode is that it is a soft polymer that
forms in situ, or within the brain, unlike
metal electrodes that are harsh and rigid,
and require open skull surgery,” Biesmans
said. Any implant in the human body
that does not belong there runs the risk
of causing inflammation and inducing an
immune response that will try to fight the
implant. Current standards for inducing
artificial electrical currents in the brain,
such as gold electrodes, are not optimal.
Biesmans’ team’s primary goal was to
develop a "softer" alternative that could be
formed within the body.
Their approach was to create a gel
mixture that, once injected into the brain,
could self-assemble into a polymer that was
able to restore electrical activity. There’s a
popular saying that "the answer you seek is
within you," and that’s the advice that the
researchers followed. Previous researchers
at Stanford had used an outside solution—
genetic modification—to produce soft
electrodes. However, this pathway comes
with its own problems when it comes to
human application due to ethical concerns
over modifying human DNA. “With our
simple injectable gel, there’s no need for
genetic modification. And in the long
term, maybe there is also no more need for
open skull surgeries,” Biesmans said.
This gel cocktail concoction is composed
of monomers, or building blocks, as well
as enzymes that will be used to make the
polymer electrode. The powerful part of
this research is that it takes advantage of
the enzymatic breakdown of two types
of biological sugars found in the body to
assemble these monomers into a polymer
electrode. First, glucose or lactate—
two types of sugars in the body—are
converted into hydrogen peroxide by
common enzymes known as oxidases.
Next, hydrogen
peroxide is used
by horseradish
peroxidase (HRP),
a naturally
occurring enzyme,
to start the
p o l y m e r i z a t i o n
process. And that’s
it—a simple, twostep
process links
together the monomer
components from the
injected gel to form a soft
electrode directly in the body.
But even the coolest products still
need to be tested for quality, and that’s why
Biesmans and her team came up with a set
of seven criteria ranging from fluidity to
biocompatibility and stability to assess the
electrodes. The first test they ran assessed
the effectiveness of their injected electrode
gel on 0.6 percent agarose gels, which is a
well-known model for simulating brain
chemistry and conditions. “In the early
stages of research, if you don’t know
much, you don’t want to go straight to
zebrafish or animal models because you
don’t know what works yet,” Biesmans
said. In this initial stage of testing, the
researchers went through at least fifty to
sixty different injectable electrode gels to
find a few that were promising enough to
continue working with. “Some gels were
too thick and did not even make it into the
agarose gels,” Biesmans said.
The team then moved on to
demonstrating the conductivity,
28 Yale Scientific Magazine May 2023 www.yalescientific.org